The power supplies in a computer system are designed to meet the specific power requirements of the integrated circuit chips (ICs) that are the components of the system. The nominal operating voltages for the ICs are typically known because most ICs are manufactured to meet industry standards for device operation. For example, common nominal supply voltages include 5.0 volts and 3.3 volts.
When an IC having a different nominal operating voltage is used in a computer system, a DC--DC converter may be used to convert a DC input voltage to a desired DC output voltage. DC--DC converters may be broadly classified as linear voltage regulators and switching voltage regulators, and switching voltage regulators may be further classified as pulse-width-modulated (PWM) converters and resonant converters. Switching voltage regulators are often preferred over linear voltage regulators due to their superior efficiency.
FIG. 1 shows a DC--DC converter according to the prior art. The DC--DC converter 100 includes a switching regulator circuit 110, a power switching transistor 115, and an output stage 120 that provides a DC output voltage V.sub.out to the IC 105. The DC output voltage V.sub.out output by the output stage 120 is fed back to the switching regulator circuit 110. The switching regulator circuit 110 is often a commercially available IC that provides a drive signal for switching the power switching transistor 115 on and off in response to the sensed value of V.sub.out. The switching regulator circuit 110 typically includes an internal oscillator circuit that outputs the drive signal at a fixed frequency. The switching regulator modulates the pulse width of the drive signal to vary the amount of time that the power switching transistor 115 is switched on. When switched on, the power switching transistor 115 couples the DC input voltage VDD to the output stage 120. The DC output voltage V.sub.out is a function of the duty cycle of the switching regulator circuit 110 and DC input voltage VDD. For example, if the switching regulator circuit 110 causes the power switching transistor 115 to be on sixty percent of the time, the DC output voltage V.sub.out supplied to the IC 105 by the output stage 120 is approximately equal to sixty percent of VDD.
When tight regulation of the DC output voltage V.sub.out is desired, the use of a commercial IC as the switching regulator circuit 110 can increase the cost of the DC--DC converter 100 significantly. However, the use of a switching regulator IC often provides high efficiency regulation and requires few components to implement. It is therefore desirable to provide a new type of high precision, reduced cost switching regulator circuit that provides similar or improved performance when compared to switching regulator circuits and ICs of the prior art.